In a forming process of an organic light emitting diode (OLED) display screen, a high-precision metal mask plate is usually used, and an evaporation material is heated there under to make the material evaporate or sublimate upward and penetrate through a pre-designed opening of the mask plate and deposit on a surface of a substrate to be evaporated to form a pattern of a desired film layer.
The mask plate commonly includes masks and shielding films, the masks and the shielding films are all need to be welded on a frame. A plurality of masks needs to realize a combination with the frame, that is, to realize stretching. Each of the shielding films is welded on a gap between adjacent two masks to play a function of shielding the gap to prevent the material from being evaporated to the substrate from the gap and resulting in a color mixture or a contamination of the substrate.
In general, welding of stretching is performed according to the following steps: first, the shielding film is welded on the frame, and then the mask is welded, and because of the existence of an overlapped connection between the mask and the shielding film, welding may not be performed, and an edge of a thinner mask easily be wrinkled or curled, which lowers a yield rate of evaporation.
Once a defect of stretching occurs or a usage defect of the mask occurs due to having been used for a long time, the mask needs to be replaced, therefore it is necessary to tear the mask and the shielding film out from the frame and polish a welding point of the frame. Since there is a higher requirement for flatness of the welding point, in general, a usage period of the frame is 2˜3 times, after this period, the frame may not be reused.